The Google Now on Tap feature on Android Marshmallow lets you get information based on the active app or screen. to turn off or disable Google Now on Tap on your Android device, do as follows:
1. Make sure your are running the Android Marshmallow and the Google app is up to date
2. Open the Google app from the app drawer
3. Tap the 3line icon followed by the Settings.
4. Tap the Now Cards option
5. Make sure to disable the Now on Tap toggle button to turn off Google Now on Tap feature.